Hi Matt,
With heavier gear, it is vital that the end of the line ends up in the right place. Make a higher lift slightly in bank before you make your circle. What you have done wit increasing circle size is right, from the higher & slightly in bank position you will be able to make the circle and clear the line without having to move the tip upstream at all before you make the circle. With a circle cast or snap T, the point of the snap and or apex of the circle has a lot to do with how far up or down stream the end of the line will land.
Sounds to me as if you were being left with a bloody L due to the line being positioned too far upstream.
Imagine a scribing a U turned on its side for your circle, so it has a top leg and a bottom leg with the bend of the U pointing upstream. If you lengthen the top leg and shorten the bottom leg as you make your circle you will get a lot of line upstream and you will not be able to turn it into your D and straighten the leader.
Does that make sense?
Cheers
Ben